This invention relates to container end closures such as tops or bottoms made of a combination of paperboard and plastic materials, and especially to tops and bottoms used with tubular containers.
Tubular containers find use throughout the packaging industry and provide a robust container useful in a broad range of applications to hold a wide variety of bulk goods including foodstuffs, hardware and chemicals to cite only a few examples.
Tubular containers typically comprise three separate components, the tube forming the sidewalls of the container, a top for sealing one end of the tube and a bottom for sealing the opposite end. Separate components for one or both closures are often used primarily because it is not practical to integrally form a top or bottom with the tube. This is especially true if an air-tight seal is required or flat bottoms and tops are desired to allow the tube to stand upright or stack atop another tube.
Having three components complicates the process of filling and sealing tubular containers and increases their unit cost in comparison with, for example, box containers wherein the tops and bottoms are integral with the container sidewalls.
Tubular containers require that separate bottoms and tops be supplied and somehow be attached and sealed to the tubular sidewall. Liquid hot-melt adhesives provide an effective attachment and sealing means, but they add a further expense to the processing in the form of adhesive costs and capital investment in machinery required to handle and apply the adhesive to the tops and bottoms. The cost increase per container incurred by the use of liquid hot-melt adhesives to form tubular containers is unacceptable to many manufacturers and makes tubular containers uncompetitive with other types of containers. A further disadvantage associated with liquid hot-melt adhesives is the potential for contamination of the container contents when the liquid is applied to attach and seal the top or bottom to the container.
Another disadvantage of tubular containers sealed by hot-melt adhesives becomes apparent after the container is filled with product and the second closure, be it the bottom or the top, is to be attached and sealed closed. Machinery which may come into contact with the product must be built to withstand product spillage, must not contaminate the product, and must not cause dangerous conditions, for example, cause open sparks in the presence of fine powders which could lead to an explosion. (Machines which handle foodstuffs are built to especially rigorous standards imposed by the FDA.) These requirements lead to machines which are considerably more expensive than machinery which must merely form the container and attach a closure to one end. It is, therefore, highly desirable to physically separate the machine which attaches and seals the second closure to the filled container from the machine which forms the container. It is also advantageous to make the machine which seals the closure to the container as simple as possible, preferably, impervious to the product and easily serviced and cleaned in the event of an accident. This is not generally possible when liquid hot-melt adhesives are used.
There is clearly a need for tubular container closures which are attachable and sealable without using liquid hot-melt adhesives and by relatively simple machinery which is impervious to spillage and will not contaminate the product.
The invention concerns both a closure for a container as described and claimed herein and a container having such a closure.
The container, preferably a spiral wound tubular type, has a sidewall defining an interior and an end opening. The preferred embodiment of the closure comprises a central panel positionable in registration with the opening. The central panel has a perimeter substantially conforming to the container sidewall. At least one secondary panel extends angularly from the perimeter of the central panel and forms a surface around the closure substantially parallel to and facing the sidewall of the container. A metal foil layer is adhered to the surface formed by the secondary panel. The metal foil layer has a side facing the sidewall on which a heat-activated adhesive layer is positioned. The adhesive layer is engageable with the sidewall, and the metal foil layer is heatable by electromagnetic induction to melt the heat-activated adhesive layer and form an adhesive bond between the secondary panel and the sidewall when the secondary panel and the sidewall are in interfacing relationship.
Preferably, the surface formed by the secondary panel faces outwardly from the central panel and engages the container sidewall within the interior of the container, the closure interfitting within the container like a plug. Preferably, the closure also comprises a plastic skirt extending around the perimeter of the central panel. The skirt has an upper leg adhered to the central panel and a lower leg adhered to the secondary panel on a side opposite to the heat-activated adhesive layer.
In the preferred embodiment, the sidewall, central panel and the secondary panel all comprise paperboard, the metal foil layer comprises aluminum, and the heat-activated adhesive layer comprises a plastic resin.
When the closure is being used as a top for the container, a first portion of the secondary panel surface is preferably removably attached to the sidewall, and a second portion of the surface is fixedly attached to the sidewall. The adhesive bond between the first surface portion and the sidewall is a relatively weaker bond than the adhesive bond between the second surface portion and the sidewall. This allows the first surface portion to define a movable part of the closure which is relatively easily separable from engagement with the sidewall and movable with respect to the container. The second surface portion defines a fixed part of the closure intended to be permanently attached to the sidewall. A hinge is positioned on the central panel between the fixed and movable parts of the closure. When the closure is positioned in registration with the opening, the movable part is pivotable on the hinge relatively to the fixed part into a position away from the opening to expose the opening and allow access to the contents of the container.
The relatively weaker bond associated with the first surface portion may be formed by positioning an adhesive release agent at an interface between the first surface portion and the container sidewall. Preferably, the adhesive release agent is positioned at the interface between the adhesive layer and the foil layer, although other interfaces, such as between the aluminum foil and the secondary panel, are also feasible. The weaker bond may also be formed by incorporating a raised region of reduced surface area on the first surface portion. The raised region projects above the surface of the secondary panel toward the sidewall and has a surface area comprising a fraction of the surface area of the first surface portion. The relatively weaker adhesive bond is caused by the reduced surface area interface between the first surface portion and the sidewall and is formed between the foil layer covering the raised region and the sidewall.
In an alternate embodiment, the closure comprises a removable lid having a central surface in overlying relation with the central panel of the closure. The removable lid has a perimetral flange extending angularly outwardly from its central surface around the lid, the flange conforming substantially to the plastic skirt. The skirt has a rim positioned surrounding the closure, the rim defining a shoulder extending inwardly toward the lid and engaging the perimetral flange substantially around the lid for removably retaining the lid to the closure.
The invention also concerns a method of manufacturing a closure sealable to a container by electromagnetic induction. The method comprises the steps of providing a substrate layer having a layer of metal foil adhered to one side thereof and a heat-activated adhesive adhered to the metal foil layer opposite said substrate layer. Preferably, the substrate layer is paperboard, the metal foil is aluminum and the adhesive is a plastic resin. Another step of the method includes forming from the substrate layer a central panel having a perimeter and at least one secondary panel extending from the perimeter. The central panel is designed to fit in registration with an opening of the container. In a further step, the secondary panel is angularly oriented with respect to said central panel and an elastic skirt is formed around the perimeter of the central panel, the skirt having at least one leg positioned on a side of the secondary panel opposite to the metal foil layer. The orienting and forming steps are preferably done in a core and cavity mold, and the skirt is formed from a plastic resin via injection molding using the aforementioned mold. Preferably, the central and secondary panels are formed by die cutting the substrate layer.
It is an object of the invention to provide a closure for a tubular container.
It is another object of the invention to provide a closure for a tubular container attachable to the container without the use of liquid hot-melt adhesives during filling and assembly of the container.
It is yet another object of the invention to provide a closure attachable to a sidewall of a container by means of induction heating.
It is still another object of the invention to provide a closure having a fixed portion and a movable portion for forming a hinging lid for the container.
These and other objects of the invention will become apparent from a consideration of the drawings and detailed description of the preferred embodiment.